1. Field of the Invention
The present invention relates to a method for preparing a mineral wool product. The products according to the invention are intended for use as for instance thermal and fire insulation, fire protection, noise reduction and regulation growth media reinforcement of other materials such as plastics, and fillers. In particular the present invention relates to method for manufacturing a mineral wool product wherein use is made of a phenol-formaldehyde resin as curable binder.
2. Description of Related Art
Resin preparations based on phenol-formaldehyde resin are well known in the art as thermocurable binders. The resin preparation can be used in a non-polymerized or partly polymerized form. The resin preparation is atomized into a gas flow and after contact with mineral fibres is deposited thereon and cured by a temperature treatment, whereby the mineral wool-containing fibres are mutually joined by the cured resin.
The phenol-formaldehyde resin contains both phenol and formaldehyde in a molar ratio of 1:2.8 and more, such as up to 1.6. In general the quantity of formaldehyde is over the stoichiometric amount, such as in the ratio 1:3.1 to 1:5, for instance 1:3.4. The excess of formaldehyde avoids the possibility of phenol remaining present in gaseous form in the gas flow and being emitted to the environment after atomizing of the resin preparation and evaporation of the water present therein.
The resin preparation generally also contains ammonia for the purpose of binding the excess amount of formaldehyde relative to phenol with the formation of ammine compounds such as hexamethyl tetra-ammine.
A drawback to the use of such a phenol-formaldehyde resin and ammonia-containing aqueous preparation is the emission of ammonia in quantities of up to 200 ppm.
The present invention has for its object to provide a solution to this drawback of ammonia emission which is less expensive than the usual method for removing ammonia from gas, for instance by means of using scrubbers. This is however subject to the condition that the curing of the phenol-formaldehyde resin is substantially not adversely affected and the emission of phenol and/or formaldehyde substantially does not increase.